1. Field of the Invention
The present invention relates to a label switching router (LSR) having an internal channel share function over an ATM which sets up internal channels in advance and shares internal channels when an external channel needs to be set up, and a method for sharing an internal channel using the same.
2. Description of the Related Art
In general, an Multiprotocol Label Switching network (or MPLS network) improves transmission of layer 3 (L3) packet by an internet protocol (or IP) header used in an existing local area network/wide area network (LAN/WAN), and thus efficiently and rapidly transmits the L3 packets by using a new label stack having a short length, namely an MPLS header. The connection structure of the MPLS network includes an end system for performing a router function, and LSRs classified into label edge routers (LER) positioned on contact points to the existing network, and core LSRs positioned in the MPLS network according to their functions.
An MPLS control protocol stack for supporting MPLS functions includes a label distribution protocol (LDP) layer for transmitting/receiving label values between the LSRs. An MPLS, also called a label switch path or LSP, is set up to transmit the L3 packets by the corresponding LDP layer according to the MPLS. In the ATM MPLS network, when the L3 packet is transmitted from the existing network such as the LAN through ATM (or Asynchronous Transfer Mode) access such as an IP over ATM (or IPOA) of the end system, an MPLS layer of an ingress or incoming ATM-LER positioned on the boundary of the ATM MPLS network transforms the L3 packet into ATM cells, and transmits the ATM cells to a core ATM-LSR through an ATM LSP determined by an LDP layer. Identically to general ATM cell transmission, the core ATM-LSR transmits the ATM cells to an egress or exiting ATM-LER by VPI/VCI (or virtual path identifier/virtual channel identifier) switching of the ATM cells in an ATM layer. The egress ATM-LER assembles the ATM cells into L3 packet and transmits the ATM cells to the existing network through the end system.
In order to set up an external channel such as the LSP or IPOA PVC (or permanent virtual circuit), the virtual path (or VP) tunnels are set up in the form of a VP full mesh in the ATM MPLS network. That is, the ATM MPLS network sets up the VP tunnels by using the internal channel set process due to the external channel. When one external channel LSP or IPOA is set up, the internal channels must then be connected as many as the value obtained by subtracting the set Forwarding Engines (or FEs) 200 from the whole FEs 200. Accordingly, when N LSPs are set up, a number of channels required in the ATM MPLS network is represented by following formula 1:Network channel number=external channel number (N)+N*(FE number−1)  <Formula 1>
Considering the mapping relations between the internal and external channels, the general internal channel allocation restricts capacity of the ATM MPLS network. For example, when 16K of LSP and 16K of IPOA PVC are needed per 622 Mbps of FE in 10 G of MPLS network, 512K of channel capacity is required to set up channels. However, channel capacity per 622 Mbps is restricted to 64K, which influences the ATM MPLS network.